This directory is for the custom SVG filters.
Inkscape loads filters from all SVG files here at runtime
and makes them accessible via the Effects > Filters and its submenus.

Each filter must have attributes:

inkscape:label is the name in the menu
inkscape:menu  is the submenu under Effects > Filters
inkscape:menu-tooltip is the menu command's tooltip in the statusbar

These are then put into filters.svg.h in order to make them translatable.
They should appear as a normal translation to translaters through the
gettext system.